Determination of start-up curves for a boiler with natural circulation based on the analysis of stress distribution in critical pressure components

•Accelerating the start-up of a boiler with the natural circulation was proposed.•The paper presents the start-up for boiler from the cold, warm, and hot states.•The optimum start-up curves for the boiler were determined.•The European Standard EN 12952-3 and the method proposed by the authors were used.•The boiler start-up time can be shortened from 6.5 to approximately 2 h.

The paper concerns the possibility of accelerating the start-up of a steam boiler with the natural circulation. Shortening the start-up time will reduce start-up losses, including support fuel consumption. The paper presents the start-up for boiler from the cold, warm, and hot states. Using the European Standard EN 12952-3 permissible heating and cooling rates were determined for thick-walled components of the boilers, i.e. drums and the live steam outlet header. The pressure and temperature curves for the drum and outlet header of the boiler were also found. Moreover, a new method of the optimum heating of boiler drums proposed by the co-authors of the paper was used to determine optimum temperature and pressure changes of the fluid. In the proposed method of the heating optimization of boiler pressure components, abrupt fluid temperature changes are allowed at the beginning of the heating process. The calculations performed by both of these procedures, the Standard EN 12952-3 and proposed method, indicate that the boiler start-up time can be shortened from 6.5 to approximately 2 h.